1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for detection of substrate warping during rapid thermal processing.
2. Description of the Related Art
Although annealing in early stages of silicon technology typically involved heating multiple wafers for long periods in an annealing oven, rapid thermal processing (RTP) has been increasingly used to satisfy the increasingly stringent requirements for increasingly smaller circuit features. RTP is typically performed in single-substrate chambers by irradiating a substrate with light from an array of high intensity lamps. The radiation is absorbed by the substrate and quickly heats it to a desired temperature, such as above 600 degrees Celsius. The radiant heating can be quickly turned on and off to controllably heat the substrate over a relatively short period of time, e.g., a few seconds.
During RTP processing, particularly during initial recipe setup processes, non-uniform substrate heating may occur. Rapid, non-uniform heating of the substrate results in warping of the substrate. In addition, due to the typically narrow gap between the substrate and a reflector plate situated above (or below) the substrate, the warped substrate may contact the reflector plate while the substrate is rotating. Force from this contact may lead to a number of undesirable results, such as moving the substrate from its support, scratching the substrate, or breaking the substrate.
Therefore, there is a need for effective methods and apparatus for detecting substrate warping during RTP to reduce the risk of substrate and/or equipment damage.